Voltage

Engineering

Chopper

Amplifier

Capacitor

Physics

Mathematics

Electronic engineering

CMOS

Optoelectronics

Electrical engineering

IEEE Journal of Solid-State Circuits

A capacitively-coupled chopper instrument amplifier (CCIA) for bio-potential monitoring analog front-end (AFE) with auto-calibrated dual positive feedback loops (DPFLs) is presented in this article. The proposed AFE with the DPFL does not only prevent total input impedance degradation by unexpected external and internal parasitic capacitances but also achieves excellent noise efficiency simultaneously. The DPFL consists of a conventional internal positive feedback loop with an attenuator for enhancing calibration resolution and an external positive feedback loop outside of the input chopper to compensate for a large external parasitic capacitance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C_{P-EXT}$ </tex-math></inline-formula> ), boosting total input impedance significantly. To precisely determine the feedback factor of the DPFL with respect to parasitic capacitors, an on-chip foreground calibration is also implemented in this work. Fabricated in a 110-nm CMOS process, the prototype AFE consumes 3.83 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{W}$ </tex-math></inline-formula> per channel at 1 and 1.5-V supplies and has the input-referred noise of 0.36 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{V}_{rms}$ </tex-math></inline-formula> from 0.5 to 300 Hz with the noise efficiency factor of 1.54. The proposed AFE achieves high-input impedances of 15 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{G}\Omega $ </tex-math></inline-formula> at 10 Hz and 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{G}\Omega $ </tex-math></inline-formula> at 50 Hz, even with an additional <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C_{P-EXT}$ </tex-math></inline-formula> of 82 pF.

A 3.8-<i>µ</i>W 1.5-NEF 15-GΩ Total Input Impedance Chopper Stabilized Amplifier With Auto-Calibrated Dual Positive Feedback in 110-nm CMOS

A 3.8-µW 1.5-NEF 15-GΩ Total Input Impedance Chopper Stabilized Amplifier With Auto-Calibrated Dual Positive Feedback in 110-nm CMOS